JPH053561B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a near-infrared light transmitting material that has excellent transparency in the near-infrared region.

More specifically, by reducing the absorption loss inherent to the material at specific wavelengths in the near-infrared region, we have developed an epoxy resin composition suitable for micro-optical components such as microlenses that have increased light transmittance at wavelengths of 1 μm or more. The present invention relates to a near-infrared light transmitting material.

[Prior Art] Development of optical communication systems using optical fibers is progressing at a rapid pace in preparation for the information society that has progressed in recent years.

The core of current optical communication systems is near-infrared optical communication systems that use optical fibers as transmission paths and transmit near-infrared light of 0.8 μm or more, and the materials used for these systems are quartz glass, etc. various types of glasses, electro-optic crystals such as lithium niobate.

Compared to the widespread use of organic materials in the electronics field these days, the use of organic materials in the optical communications field is extremely rare.This is because there is almost no data on organic materials in the near-infrared region, making it difficult to determine whether or not to use them. This is because it is a big deal.

[Objective of the Invention] While studying the optical properties of organic materials in the near-infrared region, the present invention aims to develop materials with excellent light transmittance in the wavelength range that is used or expected to be used in optical communications. As a result of research to obtain this, the present invention has been arrived at.

[Structure of the Invention] The wavelength of light used for optical communication depends on the loss characteristics of the quartz optical fiber and the semiconductor laser.

The wavelength bands currently used for optical communications are 0.8 to 0.9 μm, where the loss of optical fiber is relatively low, and 1.1 to 1.35 μm, which is a low loss range of 1 dB/Km or less, and 0.2 dB/Km.
There are three wavelength bands of 1.55μm, which is an ultra-low loss region of less than Km.

When we examined the loss spectra of various organic materials in these three wavelength bands, we found a large absorption peak in the wavelength range centered on 1.2 μm, which will be most frequently used in the future.

Analysis revealed that this is due to higher harmonics of C-H stretching vibrations of hydrogen bonded to the carbon of a saturated carbon-carbon bond, such as methyl group (-CH ₃ ), methylene group (>CH ₂ ), etc. .

The absorption by C-H stretching vibration of saturated hydrocarbons is
It appears at 3.37 to 3.5 μm, while absorption due to C-H stretching vibration of aromatic and other unsaturated hydrocarbons appears at 3.3 μm or less, for example, at 3.25 to 3.28 μm for benzene.

These third harmonics appear in a wavelength range that is slightly different from the calculated value due to anharmonicity, but the former is 1.17~
1.18 μm, and the latter is around 1.12 to 1.14 μm.

About polymethyl methacrylate (PMMA), which is currently the most transparent and widely used material in the visible range.
Looking at the absorption in the 1.2 μm region, a peak with an absorption maximum at 1.175 μm is observed, and the tail of the peak extends to 1.2 μm.

Assuming that the spectral half-width of a semiconductor laser is 20 nm with a margin, the absorption peak at 1.175 μm is extremely harmful.

Furthermore, when considering the breakdown of the insertion loss of optical components, there are absorption loss due to the material, scattering loss, and Fresnel reflection loss at the connection surface.

Scattering loss is limited to near-infrared light with a wavelength of 1 μm or more, and if the material is filterable, it is possible to remove a large amount of impurities of 0.5 μm or more, and Rayleigh scattering is the fourth power of the wavelength. Since it is proportional to 1, it cannot be a major loss factor.

Furthermore, if the interface is smooth and the optical axis is perpendicular to the surface, the Fresnel reflection loss will be about 0.1 dB at most even if the difference in refractive index is large, and this will not result in a large scattering loss.

However, the absorption loss inherent to the material is proportional to the optical path length according to Lambert-Beer's law, and the transmittance in the wavelength range where absorption occurs is low.
This poses a major hindrance to the design of optical components.

As described above, in order to obtain a material with improved transmittance, it is first necessary to reduce the absorption loss inherent in the material.

Here, the present invention provides a material with excellent transmittance in the near-infrared region, particularly in the 1.2 μm band, and shows a specific method for obtaining an optical component suitable for near-infrared optical communication.

The present invention has a hydrogen functional group concentration (mol/) bonded to a carbon atom of an aliphatic and/or alicyclic carbon-carbon saturated bond of 60 mol/
The present invention relates to a near-infrared light transmitting material having excellent near-infrared light transmittance, which is characterized by the following characteristics.

The near-infrared light transmitting material used in the present invention has a hydrogen concentration of aliphatic or alicyclic CH bonds, that is, a hydrogen concentration of methyl groups (-CH ₃ ), methylene groups (>CH ₂ ), etc., of 60 mol/or less. Certain organic materials, especially plastic materials.

The hydrogen functional group concentration referred to here was determined by the following formula (1).

Hydrogen functional group concentration = number of hydrogen atoms such as CH ₃ groups, CH ₂ groups / molecular weight (or molecular weight of monomer unit) x density (g/
cm ³ ) × 1000…(1) The hydrogen functional group concentration expressed by formula (1) is 60 mol/
It must be less than or equal to, and if it exceeds
The absorption loss of 1.17 to 1.18 μm becomes large, and there is a lack of freedom in design as an optical component for optical communication, making it unsuitable for use.

Plastics with a structure mainly consisting of aromatic rings are suitable as such organic materials, and plastics with a structure in which the hydrogen of a methyl group, methylene group, or methine group is replaced with a halogen element such as fluorine or chlorine or deuterium are suitable. Preferred are plastics with a

Here, if a halogen element other than fluorine is contained, the refractive index will increase, and there is a concern that Fresnel reflection loss will increase in connection with a glass optical fiber.

However, now the incident light power Pi of the transmitted light power Pt
The ratio to is expressed by equation (2).

(Here, φ ₁ is the incident angle, and n ₁ and n ₂ are the refractive index of the medium.) Here, n ₁ is the refractive index of quartz, which is 1.46, and n ₂ is the refractive index of the organic material, which is estimated to be 1.7. Fresnel return loss (-10logPt/Pi) is about 0.025dB (0.58%) even if some axis deviation is considered.

This value is insignificant compared to the absorption loss inherent to the material.

As a plastic whose main structure is an aromatic ring,
There are so-called engineering plastics such as bisphenol A polycarbonate, polysulfone, and polyetheretherketone, and there are also aromatic epoxy resins such as bisphenol A skeleton.

Epoxy resin has the following characteristics compared to the engineering plastics mentioned above.

By selecting an epoxy resin, a liquid composition with low viscosity at room temperature can be obtained.

Various variations can be obtained by combining the epoxy resin as the main ingredient and the curing agent, and the hydrogen functional group concentration represented by formula (1) can be adjusted in various ways.

If an acid anhydride is selected as the curing agent, purification in a heated state is also possible.

Furthermore, the heat resistance of the curing agent is also very high, making it a very useful material for the purpose of the present invention.

In the epoxy resin composition, the epoxy resin is bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, tetrabromobisphenol A diglycidyl ether, hexafluorobisphenol A diglycidyl ether, etc., and the curing agent is m-xylene diamine, Nadic anhydride (5-norbornene-2,3 dicarboxylic anhydride), chlorendic anhydride (1, 4, 5, 6,
7,7-hexachloro-5-norbornene-2,
3 dicarboxylic acid anhydride) and the like are suitable.

These compounds are in a liquid state in an uncured state, and impurities such as dust on the order of μm or more can be removed by passing through a filter, and scattering loss can be kept low.

Therefore, compared to the extremely high melting point of thermoplastic plastics consisting of aromatic rings, epoxy resins are much better as resins for near-infrared light transmitting materials.

When using a halogen-substituted halogenocarbon compound, the halogen concentration of halogens other than fluorine is preferably 20 mol/or less.

This is because if the halogen concentration is 20 mol/or more, the stability against heat and light will be significantly impaired.

[Effects of the Invention] When the above-mentioned near-infrared light transmitting material is used and the method of the present invention is followed, the absorption peak due to C-H stretching vibration of 1.17 to 1.18 μm is attenuated, and the tailing to the 1.20 μm band is eliminated. Alternatively, although the peak at 1.13 to 1.14 μm increases, the overall absorption peak becomes lower, and the transmittance of near-infrared light is significantly improved.

[Example] The present invention will be explained in detail below with reference to Examples.

Transmittance was measured using a monochromator G250 manufactured by Nippon Kogaku Co., Ltd. and a PbS detector manufactured by Zirco Co., Ltd.

Example Bisphenol A diglycidyl ether (trade name Epomic R-140, manufactured by Mitsui Petrochemical Industries, Ltd.)
and methylnadic anhydride (methyl-5-norbornene-2,3-dicarboxylic anhydride) and chlorendic anhydride (1,4,5,6,7,7-hexachloro-5-norbornene-2,3-dicarboxylic anhydride) The epoxy resin composition consisting of the above was heated to 80° C., was pressurized through a Tetron membrane filter with an average pore size of 0.47 μm, and then cast between two glass plates to obtain a plate with a thickness of 1.5 mm.

The concentration of hydrogen functional groups bonded to the carbon of the saturated carbon-carbon bond contained in this composition was 51 mol/, and the halogen (chlorine) concentration was 4 mol/.

The hydrogen functional group concentration is calculated as follows.

The structural formula of bisphenol A glycidyl ether is as follows, 100 parts by weight of epoxy equivalent 190 (n = 0.14), density 1.17, methylnadic anhydride 55 parts by weight of chlorendic anhydride The hydrogen functional group concentration when 30 parts by weight of
For bisphenol A glycidyl ether, 16 + 0.14 x 12 / 340 + 0.14 x 282 x 1.17 x 1000 x 100 / 100 + 55 + 30 ≒ 29.4 For methyl nadzic anhydride 10 / 178 x 1.23 x 100055 / 100 + 55 + 30 ≒ 20.5 Chlorendo anhydride acid 2/371×1.73×100030/100+55+30≒1.5 Overall, hydrogen functional group concentration=29.4+20.5+1.5≒
It becomes 51.

The results of transmittance measurements are shown in FIG. 1 and Table 1.

Comparative Example 1 Example 1 of an epoxy resin composition consisting of an alicyclic epoxy resin (trade name Celoxite #2021, manufactured by Daicel Chemical Industries, Ltd.) and methylnadic anhydride
A plate with a thickness of 1.5 mm was obtained in the same manner as above.

The concentration of hydrogen functional groups bonded to the carbon of the saturated carbon-carbon bond contained in this composition was 85 mol/.

The results of transmittance measurements are shown in FIG. 2 and Table 1.

Comparative Example 2 A plate having a thickness of 1.5 mm was obtained by injection molding polymethyl methacrylate (PMMA) (Parapet T-10-10 manufactured by Kyowa Gas Chemical Industry Co., Ltd.).

The concentration of hydrogen functional groups bonded to the carbon of the saturated carbon-carbon bond contained in this polymethyl methacrylate (PMMA) was 95 mol/.

Polymethyl methacrylate Molecular weight of monomer unit = 99 Number of hydrogen atoms in monomer unit = 8 Hydrogen functional group concentration = Number of hydrogen atoms such as CH ₃ groups, CH ₂ groups / Molecular weight (or molecular weight of monomer unit) x Density (g/
cm ³ )×1000 = 8/99×1.18×1000≒95(mo
l/) The transmittance measurement results are shown in Figure 3 and Table 1.

[Brief explanation of the drawing]

Figure 1 shows the loss spectrum of the example sample at 1.1 to 1.3 μm, and Figure 2 shows the loss spectrum of the comparative example 1 sample.
Loss spectrum at 1.1 to 1.3 μm. FIG. 3 shows the loss spectrum at 1.1 to 1.3 μm of Comparative Example 2.

【table】

Claims (1)

[Scope of Claims] 1. An epoxy resin selected from the group of bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, tetrabromobisphenol A diglycidyl ether, hexafluorobisphenol A diglycidyl ether, and m- An epoxy resin composition consisting of xylene diamine, a curing agent selected from the group of nadzic anhydride, methyl nadzic anhydride, and chlorendic anhydride, expressed in hydrogen functional group concentration (mol/) defined by the following formula. The hydrogen concentration bonded to the carbon atom of the aliphatic and/or alicyclic carbon-carbon saturated bond is 60 mol/
A near-infrared light transmitting material characterized by: Hydrogen functional group concentration = number of hydrogen atoms such as CH ₃ groups, CH ₂ groups, etc./molecular weight (or molecular weight of monomer unit) x density (g/
cm ³ )×1000 (unit: mol/)